It is well understood in the vacuum furnace art that the materials to be heat treated must be supported away from the heating element per se and preferably in a position to have all of the material to be heat treated receive heat uniformally or very nearly uniformally. In the prior art the materials to be heat treated (the loads) have been held supported by stainless steel networks of bars or solid molybdenum bars. Such an arrangement had a number of undesirable aspects such as the work baskets which sat on the bars would fuse with the bars and would expand at a different rate than the bars, thereby causing the molybdenum bars or stainless steel networks to fracture. More recently the loads have been held on a hearth composed of support bars made of graphite. The support bars have been formed with a groove, or channel, on the upper surface and into each channel there has been located a plurality of ceramic, or non-metallic, rollers. Such support bars have been located so as to be parallel to the width of the mouth of a vacuum furnace or orthogonal to the length of the hot chamber. In the foregoing configuration the load can be rolled into the hot zone. However in such a prior art arrangement, the ceramic, or non-metallic, rollers are subject to thermal shock and are readily broken under the weight of a load. To accommodate the regular breakage, the roller is divided into small segments, that is a channel of 48 inches would have 12, four inch rollers located therein. This type of hearth is described in detail in U.S. Pat. No. 3,421,747. The prior art arrangements did not turn to using metallic rollers because of the propensity of the graphite bars and metallic rollers to fuse under high temperatures. The prior art also did not turn to metallic rollers because of the eutectic effect between such metallic rollers and the baskets that carry the materials to be heat treated.
The present arrangement includes metallic rollers which neither "stick" to the graphite bars and which do not fuse with the baskets that carry the materials.